1. Field of the Invention
This invention relates to a torque sensor, more particularly to an improved torque sensor capable of noncontanctingly detecting drive torque variation as magnetostriction.
2. Description of the Prior Art
In various kinds of rotating drive mechanisms there is a need to measure torque simply and accurately since such measurement is exceedingly useful in a diverse range of industrial fields for analyzing drive mechanisms and for obtaining a better understanding of their operating condition.
Rotary drive mechanisms are used as prime movers in virtually every sector of industry, two of the most common types being automobile engines and industrial motors. In analyzing the operating condition of such mechanisms, it is important to accurately determine torque as well as the number of revolutions (rpm). Measurement of torque is particularly important in the case of automobile engines since by measuring the torque at the engine and at the transmission, propeller shaft, differential gear and other points of the power train it is possible to control the ignition timing, the amount of fuel injection, the timing for transmission shift, the gear ratio, etc. As a result of such control, it is possible to improve fuel efficiency, driving characteristics, etc.
Also in the case of industrial motors accurate torque measurement can provide data for optimizing control and diagnosis of rotary drive systems.
Conventionally, this type of torque detection has been carried out using a torque detector that detects the amount of strain arising in the rotating shaft. The torque detector of this type uses a number of strain gages bonded on the rotatry shaft and interconnected to form an electrical bridge.
With this conventional detector, however, it is necessary to machine the rotating shaft and/or its bearing in preparation for mounting of the strain gages and associated devices, e.g. a telemeter or a slip ring for electrical connection to the strain gage, and this has an adverse effect on the rotating shaft. Moreover, as a rotating shaft of this type is strongly affected by the torsional vibration of the overall power train, it is not possible to eliminate the error component introduced by the torsional vibration only by measuring the amount of strain in the rotating shaft, so that it is difficult to measure the torque with good accuracy.
To eliminate such effect of the torsional vibration, there have been developed and put to practical application torque sensors which measure the torque on the basis of the amount of strain at a rotating disk where the amount of such torsional vibration related to the overall power train is relatively small. With a torque sensor of this type, because of the decreased adverse effect of the vibrational torque, it is possible to measure the torque with higher accuracy than is possible when the measurement is based on the amount of strain in a rotating shaft as described above.
On the other hand, however, similarly to the case where the measurement is based on the amount of strain in a rotating shaft, this torque sensor also requires that a number of strain gages be bonded in place (on the rotating disk in this case) and be interconnected to form an electrical bridge. The work of attaching the strain gages is thus troublesome. Also, since it becomes necessary to provide a telemetering system, a slip ring or the like for the electrical connection to the bridge provided on the rotating disk, the measurement system becomes large and complex.